Bituminous paving material and method of producing the same



Patented Dec. 25, 1934 UNITED'STATE'S PATENT oFFlcE BITUMINOUS PAVING MATERIAL ,METHOD OF PRODUCING THES AME James F. Carla, Birmingham, Ala.

No Drawing. Application July 15, 1931, Serial No. 551,059

8 Claims. (01. 106-31) My .invention relates to a process of manufacfluxes containing a substantial percentage of volture and laying of bituminous pavements. It paratile constituents is in general to be avoided as ticularly relates to improvements in bituminous tending to produce an inferior product. It is unpaving or surfacing compositions which may be derstood also that variations from standard gradreadily stored, handled, transported and laid ings of mineral aggregates and percentages of 5 while cold, and to the processes and methods of mineral fillers may be used.

manufacturing the same. It also relates to sim- For mixtures which are to be laid cold, softer ilar compositions which are preferably reheated asphalts or bitumens having a higher penetraimmediately before being laid. tion are used than those commonly specifiedfor 10 The primary object of this invention is to efmixtures of corresponding types which are laid 10 fect greater economy and utility in the manufachot. For example, asphalts that are of sumture and use of bituminous paving compositions. ciently high penetration to be plastic at atmos- A more specific object of the invention is the pheric temperatures'should be employed. As in production of a bituminous mixture in a loose general a slightly lower percentage of total bitugranular state which may be handled and stored men is used in the mixture than is commonly 15 cold and which may be laid and compacted into used in mixtures of the same type which are to a dense, tough and durable pavement by the be laid hot. l

application of pressure, with or without a pre- The essential features of the process, of prolimin'ary heating. ducing bituminouscompositions of the charac- In the production of bituminous compositions ter herein disclosed,.and which is claimed to 20 intended to be stored, handled and transported be new and useful, consists in the :manner and cold, certain serious and well defined 'diflicuh combination of treatments of the heatedbituties and limitations have been encountered minous composition immediately after it has either or both as to the selection of bituminous been mixed in .theconventional manner, and

materials and gradings of mineral aggregates comprises the various steps in sequence, sepa- 26.

and as to their utility as paving materials. These rately and in combination with eachother, which difficulties have heretofore increasedthe cost of have for their purpose the granulation of the such compositions and limited their use for the composition as a whole and particularly the submost part to light or medium traflic pavements stantial toughening and stabilizing of the imme and to patchworkand small jobs where the indiate surfaces of the bituminous coating on the 30 creased cost of the cold mixture is lessthan the individual particles of the mineral aggregates.

cost of installing local mixing plants and other To illustrate clearly .the technical and scienfacilities for the manufacture and laying of tific principles involved, reference is made first. standard hot mixtures. i to the well known toughening and stabilizing ef- 85 In :thepractice of the present invention I am fectiof certain specific mineral fillers, as for exable to produce cold paving compositions in an ample, when finely ground limestone is incorpoeconomical mannerjfrom substantially all standrated into the body of bituminous materials, it ard combin ations and gradings of mineral agexhibits high absorptive and surface tension efgregates and mineral fillers as now commonly fects with relation to the bituminous substances.

a specified for standard types'of bituminous pave- As illustrative of this high absorptive and surface 40 ments, such as sheet asphalt, stone filled sheet tensioneiiect, it has been :discoveredthat powasphaltasphaltic concrete of the fine andfcoarse dered lime, when sprinkled into a solution of asaggregate types, includingbinders, and so-called phalt in benzol, chloroform andsimilar solvents black bases of the asphaltic concrete type, and will remove the asphalt fromthe-solution causing for treating and utilizing bituminous sandstone it to precipitate as separate particleseach comand'limestone, using standardcommercial grades prising a" lime nucleus surrounded by the asphalt. of bitumens, or .asphaltic cements, without the Similarly, :it has beenfound'that powdered lime use of volatile solvents, liquefiers, or other spewill remove asphalt from emulsions thereof. cial ingredients or treatmentsof the bituminous I have discovered after extensive investigation a or asphaltic material before mixing. with bituminous materials that when such mahis understood that properly fluxed native or terials are introduced into a water suspension of other hard asphalts may be used, as well as a hydrated lime, finely ground limestone and simismall' amount of volatile solvents if desired for lar basic and substantially insoluble materials, special purposes,but these are not essential to that a thin continuous film of the suspendedsub- I the iprocess. *I'he use of 'volatile solvents and stanceisreadilyformed or adsorbed on the sur- 5 face of bituminous material. This coating serves to render the bituminous surfaces non-sticky, within substantial ranges of pressure and temperature, and prevents the coalescence of different particles or surfaces with each other.

Accordingly, the various steps and sequence of treatments, comprising my improved process have been developed which when carried out with proper relation to each other and of temperature, produce a cooled and granulated composition in a wet or moist condition in which the immediate external surfaces of bituminous coatings are provided with a thin continuous toughened film of sufiicient stability to prevent the setting up of the mixture under all normal conditions of handling and storage, but leaving the body of the bituminous coatings sufiiciently plastic at atmospheric temperatures to permit the composition durable pavement under pressure as in rolling or tamping.

' For the purpose of forming the protective coating, finely ground material or inorganic substance containing a high percentage of the oxides, hydroxides, carbonates, or basic silicate of calcium and such magnesium as ordinarily accompanies limestone or dolomite, including bituminous limestone and basic blast furnace slags have been found to be eflicient. It is understood that other similar neutral or basic substances may be used, but clays and all substances which have a preferential absorption for water or which exhibit emulsifying properties or tendencies as between bituminous materials and water, are especially excluded as tending to produce inferior products. Only substances are selected which possess the property of being readily adsorbed by bituminous surfaces from water suspensions, and which also act as effective fillers or stabilizers of the bituminous composition when consolidated into the final pavement.

In the manufacture of the improved bituminous composition I take sand or suitable combinations of fine and coarse aggregates which are usually selected approximately in accordance with standard gradings and specifications for standard type of bituminous surfaces, binders or base courses and heat same until thoroughly dry and at a suitable temperature for mixing with bitu- 1 minous materials which Will ordinarily be found mixed material immediately into a separate cool".

ing and mixing device. For this purpose a trough conveyor of sufficient length and capacity to hold several batches from the mixer may be used. This conveyor is suitablyprovided with arevolving shaft having blades or paddles which are set at a suitable angle so as to force the bituminous mixture slowly forward while retaining it in a comparatively loose condition. On being discharged into the trough conveyor the heated loose mixture is immediately sprayed with cold water at one or more points in sufficient amount to thoroughly wet and partially cool the mixture.

At a selected point along the length of the conveyor, where the temperature has been reduced to around the softening point of the asphaltic or bituminous material, or to approximately 140 F., and the mixture thoroughly granulated by the action of the mixing blades, a quantity of finely divided mineral or inorganic material above described is added to the mixture either in a dry state or in the form of a suspension in cold water. For this'purpose I have found that a suspension of hydrated lime is preferable, though satisfactory results may be obtained with powdered limestone and other materials heretofore mentioned. In case bituminous limestone is used it is preferably added dry. Additional water is added and as the material is further mixed and conveyed forward a thin coating is formed on the surface of the bituminous films covering the particles or pieces of aggregate. to be readily consolidated into a stableand v In treating the coated aggregate with the suspension of finely divided calcareous material, care must be exercised to partially cool the coated aggregate down to near the softening point ofthe asphalt. If treated at too high a. temperature, the high absorptive power and surface tension of the calcerous material is such that it may partially remove .the coating from the aggregate. H I

It has been found that the coatings are formed chiefly from the finer particles of pulverized material and most of the coarser particles and any excess material is finally drained or washed away with the excess cooling water. Usually, the finished product will containv from one to three per cent of the fine coating material, dependingon the kind of material used and the character of the mixture. The mixture may be dischargedfrom the conveyor directly into stock piles but if not cooled to a. point substantially below the softening point of the bituminous material used it may first be discharged into cold water. Due to the great afiinity of the calcerous materials adsorbed into the surface of the bituminous material, the discharging into cold water or subsequent washing does not remove the adsorbedsurface coating. The particles thus treated remain in a loose separate condition until subjected to compressive action such as by rolling or tamping when the material is laid in a pavement. It is especially pointed out that when bituminous compositions prepared as herein described are conveyed to stock piles, the excess water rapidly drains away but a small percentage of moisture is held tenaciously for a long period of time, and this fact is an important part of the process as a contributing factor in retaining the composition in a workable condition. It has. been found, however, that the completely dried material will remain in storage for'many months without showing any substantial tendency to bond. or set up into an unworkable mass."

' The material thus treated is in especially good condition for laying in a pavement and, unless the harder grades of asphalt are employed, .re-: quires no preliminary heating before being spread and rolled upon the roadway. The compressive and kneading action on the particles when rolled forces the inner layers of bituminous materials through the outer coating of each particle and bonds it to adjacent particles, while the calcareous coating material, due to it's great surface; tension and absorptive power for the bituminous materials acts as a filler thereby toughening and increasing the stability of the pavement.

While 'I have described my invention in but one form .it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims. Also while I have described my improved product as being applicable to paving material, it will be obvious that it may be used for other purposes where a dense tough and durable material is required.

What I claim is:-

1. A process of producing a mixed bituminous material adapted to be stored in a granular condition and laid cold and to solidify upon compression, comprising, mixing hot bituminous material of sufficiently high penetration to be plastic at atmospheric temperatures with granular aggregate, maintaining said mixture in a granular condition by agitation, providing a water suspension of finely divided calcareous material, partially cooling the mixture while maintaining it in a granular condition and treating the granular bituminous material with said water suspension at a temperature near the softening point of the bituminous material.

2. A process of producing bituminous paving material adapted to be stored in a granular condition and laid cold and to solidify upon compression, comprising, mixing bituminous binder material of sumciently high penetration to beplastic at atmospheric temperatures with granular aggregate, agitating with disintegration to maintain the mixture in a granular condition, providing a Water suspension of finely divided calcareous material, treating the granular bituminous material while agitating with said water suspension at a temperature near the softening point of the bituminous material, and discharging the materials thus treated into cold water.

3. A process of producing bituminous paving material adapted to be stored in a granular condition and laid cold and to solidify upon compression, comprising, mixing bituminous material of sufiiciently high penetration to be plastic at atmospheric temperatures with granular aggregate at a temperature of from 150 to 350 F., stirring the mixed substance to maintain it in a granular condition, cooling the granular mixture until it is at a temperature near the softening point of the bituminous material, and treating it while in a granular condition with a water suspension of finely divided calcareous material.

4. A process of producing bituminous paving material adapted to be stored in a granular condition and laid cold and to solidify upon compression, comprising mixing heated bituminous material of sufiiciently high penetration to be plastic at atmospheric temperatures with heated granular aggregate, partially cooling and stirring the mixed materials to maintain them in a granular condition, and applying a coating of finely divided calcareous material to the granular particles when at a temperature near the softening point of the bituminous material.

5. A process of producing bituminous paving material adapted to be stored in a granular condition and laid cold and to solidify upon compression, comprising, mixing bituminous material of sufficiently high penetration to be plastic at atmospheric temperatures with granular aggregate heated to a temperature of from 150 to 350 F., partially cooling and stirring the mixed materials to maintain them in a granular condition, applying a coating of finely divided calcareous material to the granular particles when at a temperature near the softening point of the bituminous material, and discharging the coated granular material into cold water.

6. A ready mixed bituminous road material adapted for storage in a loose condition and to be compacted into a solidified mass upon the ap plication of pressure, consisting in mineral aggregate covered with a bituminous binder of sumciently high penetration to be plastic at atmospher'ic temperatures, and the latter having a coating of adsorbed finely divided calcareous material.

7. A ready mixed road paving material adapted for storage in a loose condition and to be compacted into a solidified mass upon the application of pressure, consisting in a granular mixture of bituminous material of sufficiently high penetration to be plastic at atmospheric temperatures, mineral aggregate and filler, and a surface coating of adsorbed hydrated lime on the bituminous surfaces of the individual particles.

8. A ready mixed road paving material adapted for storage in a loose condition and to be compacted into a solidified mass upon the application of pressure, consisting in a granular mixture of mineral aggregate filler, and bituminous binder material of sufiiciently high penetration to be plastic at atmospheric temperatures, and a coating of finely divided calcareous material adsorbed into the bituminous surfaces of the granular particles.

JAMES F. CABLE. 

